We are currently in Bruges and considering the river boat option to Damme. We had planned to cycle but the weather is a little unpredictable right now and thought the river option might be worth considering. Our main interest is enjoying the views from Brugge to Damme - and an opportunity to see a small town near Bruges. Welcome thoughts!
The Lamme Goedzak boat only sails on weekends this time of the year. Dry weather is forecast for the weekend (no rain), but with temperatures of 14°C, it's not particularly warm. Perfect cycling weather.
https://www.meteo.be/en/brugge
On the boat, you'd have to sit on the upper deck in the cold. If you sit inside in the warmth, you'll see nothing but the shore.
And with 3 Bft as the above link shows, the wind will not be too strong, I would bike to Damme. For more scenery you can go further to Oostkerke and even Sluis, just across the border in the Netherlands. And nearby charming Sint Anna ter Muiden is certainly worth the detour.
Combining biking and the boat ride is an option too. Think you can still rent bikes in Damme till the end of the month. Or rent them in Bruges and take them with you on the boat.
So there is enough room for flexibility, you can put together a trip as you like.
We cycled that last week. The weather was also unpredictable so we didn't bother booking bikes in advance and had no problems getting bikes. https://bensbike.be/ is who we used. It's an easy ride and doesn't take that long.